The present invention relates to an apparatus and method for use in respirator masks and/or rebreather hoods for absorbing noxious gases and providing an adjustable oxygen output and carbon dioxide consumption from an "at rest" level up to a high stress level, such as that which occurs during heavy work conditions.
Many devices, including respirators and rebreathers, are well known in the art whose function is to provide oxygen and absorb carbon dioxide for various uses, including health care applications, and to protect a user from airborne gaseous contaminants from fires, etc.
Such devices employ various strong chemical and physical absorbants in order to remove contaminants from gaseous or liquid streams. Chemically reactive compounds such as soda lime (ascarite) and anhydrous lithium hydroxide are carbon dioxide absorbers which are widely used. Chemical oxygen sources such as chlorates, peroxides, and alkali metal superoxides are also well known. Physical absorbents include for example, activated carbons, zeolites, silicas, aluminas and ion exchange resins.
Most devices are limited by the rate at which they provide oxygen and the conditions under which they can be used. In addition, these devices are not designed to protect the user against all types of airborne contaminants which the user may encounter. For instance, recent publications show that there are long-lived free radicals which are present in the smoke from burning organic materials. These free radicals can react with lung surfaces if they are inspired and thereby cause severe damage and even death.
Respirators commonly use cartridge-type filters containing selective absorbents for noxious gases and inspired air. These devices are designed to remove undesired chemicals and particulate matter from incoming air, enhance the oxygen level within the mask, and eliminate carbon dioxide, either directly or in conjunction with mechanical check valves. Respirators are useful only when ambient oxygen levels are at least 19.5%. For oxygen levels below this level, separate mechanical supplies of air or oxygen are used, such as tanks of compressed gases, or remote source air pumping. These devices are bulky and complicated, and the user must be trained in their proper use.
Rebreathers are a separate class of emergency use respirators, usually in hood form, which are designed to continuously absorb or remove respired carbon dioxide, and excess moisture. Rebreathers obtain their air supply from that which is trapped when the user puts on the hood. Anhydrous lithium hydroxide is often used to absorb the respired carbon dioxide. However, rebreathers have limited service life because oxygen levels are not replenished. Compressed air devices are prone to mechanical problems with release valves and the user is required to operate them properly under life-threatening conditions.
Rebreathers using moisture activated alkali metal and alkaline earth metal superoxides and the like as both an oxygen source and a carbon dioxide absorber have been tested extensively. Basically, these chemicals react readily with moisture in respired air and evolve oxygen, while at the same time providing a reaction product which will absorb carbon dioxide. Potassium superoxide is especially useful for this purpose and has been employed in many respiratory devices. However, several problems have prevented their full commercial development. One problem is a delay or start-up period which occurs before oxygen delivery begins. Also, the practical size and operating conditions of these devices place limitations on the quantities of functional chemicals and the design geometry in which they are used. Additionally, oxygen output efficiency declines significantly as the breathing rate increases. Therefore, at high stress levels, the moisture content of the respired air is inadequate to generate the necessary oxygen levels.
The above problems have been addressed in several manners. For instance, a separate injectable water source has been tested, but not successfully. In addition, compacted briquettes of the superoxide are able to provide extended oxygen delivery times, and the use of large quantities of the same are able to over-ride the efficiency loss. However, the resulting exothermic heat of reaction with water is sufficient to require external heat exchangers on the superoxide cannisters. Under these conditions, the rebreather must be physically separated from the chemical source for obvious safety reasons.
In addition to the above devices, synthetic and natural zeolites of certain composition and porous sizes are used in pressure swing absorption devices to produce commerically high purity oxygen from air. Zeolites are a family of crystalline hydrated alumino-silicate minerals, with the general formula MN.sub.2 O-Al.sub.2 O-nSiO.sub.2 -mH.sub.2 O where M is calcium, strontium or barium and N is either sodium or potassium. The ability of zeolites to function as molecular sieves, separating complex gas mixtures into various components is derived primarily from the highly uniform porous structure of the zeolite crystal which is a 3-dimensional network of interconnecting cavities. Large polar molecules are retained on the zeolite by Van der Waals forces rather than chemical bonding, while smaller and less polar molecules are not.
Air pressure well above atmospheric is required for the efficient operation of the zeolite system. In addition, since zeolites are both powerful dessicants and selective gas absorbants, the air must be pre-dried, or large excesses of zeolite must be used in order to compensate for the moisture in ambient air. In its practical use as an oxygen concentrator, the air is compressed and passed through a column of zeolite material. The more polar components of air, i.e., water vapor, carbon dioxide, and such pollutants as carbon monoxide, sulfur dioxide, nitrogen oxides, and hydrocarbons are immediately absorbed on to the uppermost layer of the zeolite, the nitrogen fraction is selectively removed, leaving oxygen, traces of inert gases and some residual nitrogen. The zeolites are the active agents in many continuous generators of oxygen-enriched air for health care applications, for example for use with patients having severe chronic obstructive pulmonary disease (COPD).
In accordance with the above, it is an object of the present invention to provide an apparatus and method for selectively absorbing undesirable organic and inorganic gases and vapors from ambient air while providing oxygen level enchancement of the treated air which is more efficient than prior are methods and devices.
It is another object of the present invention to provide unique modifications of the chemical materials commonly used in such systems to provide extended and controlled oxygen production and utilization efficiencies that allow for major reductions in the sizes and weights of the components.
It is a further object of the present invention to provide unique designs of component configurations and arrays in order to make them compatible with established breathing mask structures of both respirator and rebreather types and which can also be used in ventilating applications.
It is another object of the present invention to provide an apparatus and method which allows the activation of an oxygen generating system on demand.
It is yet another object of the present invention to provide an oxygen enrichment system which is simple and inexpensive to manufacture, safe and easily disposed after use.
It has now been surprisingly discovered that by combining the use of the above-mentioned compounds in a unique manner, the efficiency gain is much greater and different from an additive effect of each of the components.